This invention relates to pressure cookers and particularly to regulation of pressure therein.
A conventional domestic pressure cooker processes food in an aqueous environment at the temperature and pressure of saturated steam. While such processing is desirable for many food types such as stews and boiled vegetables, it does not provide the gaseous temperature environment needed for roasting or baking. An improved process of gaseous pressure cooking was disclosed by J. O. Hice in U.S. Pat. No. 3,672,908 wherein pressure is maintained above the pressure of saturated steam by a compressed gas during cooking and rapid cooling phases. Foods such as poultry, roast beef, fish, and vegetables retain flavor and moisture substantially above levels expected for conventional processing. It would be desirable to apply the Hice process to domestic food preparation but the institutional type apparatus disclosed by Hice which includes steam for heating and a refrigeration unit or liquefied gases for rapid cooling would be complex and costly. Alternative apparatus using gas or electric for for heating would still require a coolant source.
It would be desirable to extend the range of pressure cooking in gaseous environments to include a period at high temperature and low water vapor pressure to form a crisp brown skin or crust. A domestic pressue cooking appliance would then extend the range of pressure cooking beyond the gaseous environments now known for institutional food processing, yet it would provide conventional pressure cooking in aqueous environments as disclosed in my U.S. Pat. No. 4,340,111. Such versatility is more appropriate for domestic appliances where a wider variety of food types is prepared than for the more specialized institutional apparatus.
In order to combine the heating and cooling capability required for the gaseous pressure processes with the economy required for domestic appliances, it is an object to incorporate a pressure cooking appliance into a system of domestic appliances wherein each of a plurality of appliances is cooled and heated by a liquid phase thermal exchange fluid which exchanges heat with thermal reservoirs. The thermal reservoirs include a hot reservoir at a temperature of about 300.degree. C., a cold reservoir at a temperature of about -30.degree. C., and an auxiliary heat sink near ambient temperatures to utilize otherwise wasted heat. Additional details for such appliance systems may be found in my U.S. Pat. Nos. 4,164,253 and 4,173,993. Additional details for other appliances for use with such appliance systems may be found in my U.S. Pat. Nos. 4,024,904, 4,156,454, and 4,188,794.